PROJECT SUMMARY/ABSTRACT Protein kinases, of which there are over 500 in the human genome, catalyze the transfer and covalent attachment of a phosphate group from a high energy donor (e.g., ATP) to a target protein at select amino acids. One particular kinase, glycogen synthase kinase-3 (GSK-3), has over 40 protein substrates and has been implicated in a variety of diseases including pathologies of the central nervous system, pathological inflammation and metabolic disorders. Thus, there is an intense and ongoing effort to identify and develop compounds that inhibit GSK-3 activity. Lithium, commonly prescribed for psychiatric disorders, has been shown to be a relatively weak GSK-3 inhibitor. However, there are few, if any, compounds specifically designed as potent GSK-3 inhibitors that have advanced beyond clinical trials. There remains, therefore, a critical need for the development of new GSK-3-specific compounds that would be effective in treating diseases caused by aberrant GSK-3 activity. The long term research goal of this project is to discover and develop safe, and cost effective GSK-3-specific inhibitors that can be used as therapeutic agents in the treatment of human disease. Recently, the research team has identified a set of novel small organic compounds (I-GSK-3s) that potently inhibit GSK-3 activity. An extensive screen with 414 kinase assays (representing 404 unique kinases) revealed that the I-GSK-3 compounds are highly specific for GSK-3. The central hypothesis of this grant is that the I-GSK- 3 compounds represent a novel chemical scaffold upon which highly potent and selective GSK-3 inhibitors can be designed. To investigate this hypothesis, the following aims will be completed: (i) determine the mechanism by which the novel I-GSK-3 compounds inhibit GSK-3 and (ii) determine the I-GSK-3 compounds' effects on cellular GSK-3 activity. Compounds represented by this novel chemical scaffold have the potential to become therapeutics for GSK-3- mediated disease processes. The proposed work will provide a strong scientific foundation for the development of such therapeutics. Thus, successful completion of these studies will have a positive impact on the development of therapeutics for a host of human diseases including pathologies of the central nervous system, pathological inflammation and metabolic disorders.